Echo cancellers to cancel echos in a communication path are well known. A typical echo canceller generates a filter that models the transfer function of the echo signal path using a linear algorithm such as a least-mean-squared (LMS) algorithm. Network signals conveyed to the echo signal path are also conveyed to the echo canceller. The filter therein processes the network signals to generate an estimated copy of echo signals received from the echo signal path. The estimated echo signals and actual echo signals received from the echo signal path are subtracted. Differences between the estimated echo signals and the actual echo signals result in error signals, which are fed back to the echo canceller so that the echo canceller can converge to the correct transfer function.
When dealing with long delay networks, the echo signal path can change and can be different from call to call. As a result, an adaptive algorithm is required to allow the echo canceller to model adaptively the echo signal path. Unfortunately, the longer the time window or delay of the echo signals that are required to be cancelled, the longer the adaptive algorithm takes to adapt to the correct transfer function.
In addition, as the total time window increases, the number of coefficients in the filter generated by the adaptive algorithm increases, requiring more processing power. Placing conventional echo cancellers in long delay networks to cancel echos from traditional networks such as public switched telephone networks (PSTNs) or private branch exchanges (PBXs) increases the complexity and cost significantly.
It is therefore an object of the present invention to provide a novel echo cancelling system and method and a novel echo locator.